System and Method for Constructing Composite Building Boards Using Thermoplastic Films

ABSTRACT

Disclosed are building board manufacturing techniques that minimize the build-up of slurry on associated forming equipment and also produce panels with enhanced physical properties. The methods involve applying a dissolvable film laminate to one or more fiber mats at the outset of the forming process. In the undissolved state, the film acts as a containment envelope for the gypsum slurry and any free floating glass fibers. During subsequent curing, the film is dissolved by vaporized water. In its dissolved state, the film is liquefied and coats the fibers of the underlying mat. This results in a building board with improved physical properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/170,272,filed Jun. 28, 2011, and entitled “System and Method for ConstructingComposite Building Boards Using Thermoplastic Films,” now U.S. Pat. No.9,096,036, issued Aug. 4, 2015, which itself is a continuation-in-partof application Ser. No. 12/794,959, filed Jun. 7, 2010, entitled “Methodfor Constructing Composite Building Boards using Dissolvable Films,” nowU.S. Pat. No. 8,409,391, issued Apr. 2, 2013. The contents of theseapplications are fully incorporated herein for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a system and method for constructing compositebuilding boards. More particularly, the present invention relates to theuse of thermoplastic coatings in the construction of composite gypsumbuilding boards.

2. Description of the Background Art

Building board, also known as wallboard, plasterboard, or drywall, isone of the most commonly used building components in the world today.Building board is frequently used within the interior of a dwelling,where it functions both as a finished wall covering and as a structuralroom partition. Building board can also be used on the exterior of adwelling, where it serves as a sheathing to provide weather protectionand insulation. Building board can also be used as an interior facingfor other structures as well, such as stairwells, elevator shafts, andinterior ducting.

One particularly popular form of building board is known as glassreinforced gypsum (GRG) board. An example of one such board is disclosedin U.S. Pat. No. 4,265,979 to Baehr et. al. Baehr discloses a buildingboard constructed from opposing glass fiber mats with an intermediategypsum core. This construction provides a hardened external surface andis an improvement over earlier paper faced boards.

Current GRG manufacturing techniques have some significant drawbacks.Namely, during construction, some of the individual mat fibers are notcovered by the gypsum slurry core and are therefore exposed. Thesefibers have a tendency to dry out and disengage from the board. As aresult, free floating glass fibers tend to accumulate on and damageassociated forming equipment, such as forming tables, forming plates,motor drives, bearings, and the like. The presence of disengaged fibersalso presents a significant hazard to workers who must wear appropriatesafety masks so as not to ingest the fibers. The most common way tocombat this problem is through the use of expensive dust collectionequipment and/or the periodic and repeated cleaning of the formingequipment.

A subsequent board manufacturing technique is described in commonlyowned U.S. Pat. No. 4,378,405 to Pilgrim. The contents of the Pilgrimpatent are fully incorporated herein by reference. Pilgrim discloses aGRG board that is faced on one or both sides with a porous, nonwovenglass mat. The glass mat of Pilgrim is slightly but fully embedded intothe slurry core. This is accomplished by vibrating the gypsum slurry tocause it to pass through the porous openings in the mat. Embedding themat within the core as taught in Pilgrim results in a thin film ofslurry being formed on the outer surface of the board. Building boardswith this construction are referred to as embedded glass reinforcedgypsum (EGRG) boards.

EGRG boards eliminate, or greatly reduce, the presence of exposed fibersand greatly reduce the presence of free floating fibers. However, theconstruction of EGRG boards also has its drawbacks. Namely, EGRG boardsrequire the application of low viscosity gypsum slurry. This slurryleaks from the boards during manufacture and accumulates on associatedforming equipment. Thus, during manufacture, the forming tables, formingbelts, and associated rollers and motors are exposed to substantialbuild-ups of gypsum slurry. Over time, if not regularly cleaned, themanufacturing process comes to a complete stop. Thus, in traditional GRGand EGRG building board manufacturing techniques there is a substantialcapital investment in equipment designed to clean the forming areas.

Additionally, even in the construction of EGRG boards, there is acontinuing problem with some fibers becoming exposed, dried anddetached. This, in turn, results in the accumulation of free fibers onthe forming tables, forming belts and associated rollers and motors. Aswith the excess gypsum slurry, these fibers must be removed in order toprevent equipment failure resulting in downtime.

Thus, there exists a need in the art for improved building boardmanufacturing techniques. More specifically, there is a need in the artfor manufacturing techniques that minimize the accumulation of gypsumslurry and/or free floating fibers on associated forming equipment.There also exists a need to minimize capital investment needed toconstruct GRG and EGRG building boards. There is yet another need toeconomically produce GRG and EGRG building boards with improved physicalcharacteristics. The present invention is aimed at achieving theseobjectives.

SUMMARY OF THE INVENTION

One advantage of the present method is realized by applying athermoplastic film to the surface of a composite building board.

Another advantage is achieved by applying a thermoplastic film to thesurface of a building board in an in-line manufacturing process.

Another advantage is accomplished by limiting the build-up of slurry onforming equipment associated with board production.

Yet another advantage is achieved by constructing fiber reinforcedbuilding boards that minimize and/or eliminate the presence of exposedand/or free floating fibers.

Still yet another advantage is accomplished by forming a thin slurrylayer between a mat and an adjacent thermoplastic layer.

Another advantage is attained by using a thermoplastic layer in theconstruction of building boards, wherein the layer acts as a containmentenvelope for slurry and glass fibers.

Still yet another advantage is realized by forming a building boardusing an outermost thermoplastic layer, wherein the thermoplastic layerminimizes slurry leaking from the face of the board.

Still yet another advantage is that, once produced, the boards obtain athermoplastic layer that may be utilized as a base layer for additionalcoatings or surface treatments. The use of an existing plastic layer inthis manner can be in reduction of additional coating weights,modification of texture and or compounding with secondary coatinglayers. All of these advantages lead to more economical panel productionand increased panel functionality and customization.

Various embodiments of the invention may have none, some, or all ofthese advantages. Other technical advantages of the present inventionwill be readily apparent to one skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is an elevational view of the first part of the manufacturingprocess wherein the slurry is supplied between facing mats;

FIG. 2 is an elevational view of the second part of the manufacturingprocess wherein the building panels are dried.

FIGS. 3 a-3 e are successive cross sectional views of the buildingpanels taken from FIG. 1.

FIG. 3 f is a bottom plan view of the board showing the slurry bleedingthrough the board surface.

FIG. 4 is a detailed view of the curtain coater and/or slot die coaterused in applying a thermoplastic layer.

FIG. 5 is a detailed view of a spray coater used in applying athermoplastic layer.

FIG. 6 is a detailed view of a knife coater used in applying athermoplastic layer.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to a system and method for manufacturingthermoplastic coated building boards. The system and method can be usedto produce both glass reinforced gypsum board (GRG) and embedded glassreinforced gypsum board (EGRG). The thermoplastic coating is applied toa mat prior to board formation. The coating can be applied in-line oroff-line with respect to the remaining production line. The coating actsas a containment envelope between an exterior, or contacting, surface ofthe mat and the underlying forming belt. The coating also retains a thinlayer of gypsum slurry on the exterior surface of the mat. This reducescontamination of the production line and produces boards with increasedphysical properties.

FIG. 1 illustrates a gypsum board production line 20 that has beenmodified in accordance with the present disclosure. Line 20 includes aseries of forming tables 22 for supporting the building panel 24 duringits formation. As is known in the art, the mats that form panel 24 areunder tension by way of a series of downstream belts. Once panel 24 hasbeen formed, it is passed to a series of board dryers 26. Dryers 26function in driving out excess moisture and causing the gypsum slurry toset. This results in the formation of a dried composite panel 24.

As further noted in FIG. 1, gypsum board 24 is formed from first andsecond mats (28 and 32) between which a volume of gypsum slurry isdeposited. These mats are initially stored in large rolls (28 a and 32a) that are unwound to provide a continuous length of mat. First roll 28a is unwound onto forming table 22. Slurry 34 is thereafter depositedupon the mat from an overhead mixer 36 at various downstream locations.Second roll 32 a is ideally positioned downstream of first 28 a roll andis unwound over top of the deposited gypsum core to create sandwich orpanel.

Mats (28 and 32) are preferably constructed from a series of nonwoven,randomly aligned glass fibers. Mats (28 and 32) may also comprisecontinuous or non-continuous fibers, organic or inorganic fibers, wovenor nonwoven fibers, or blends thereof. The fibers may also be continuousin length, chopped non-continuous in length, identical or random inlength, of blends thereof. The fibers within mats (28 and 32) ideallyhave lengths of between ½″ to 2.″ Mats (28 and 32) preferably have athickness of between about 0.0625″ to 0.5″

Mats (28 and 32) are also preferably pre-coated with an organic orinorganic resin binder to hold the individual fibers together.Additionally, mats (28 and 32) can be supplied uncoated, with the resinbinder being applied at a point along production line 20. However, thedisclosed method can be carried out with a variety of other matconstructions.

In accordance with the present disclosure, a volume of hot, moltenthermoplastic 38 is applied to an external surface 40 of first mat 28prior to forming table 22. More specifically, as noted in FIG. 1, firstmat 28 is routed by way of guide rollers 42 beneath a coating device 44,which applies a uniformly thin layer 46 of liquefied plastic 38 overexternal surface 40 first mat 28 in a continuous in-line process. Any ofa variety of hot melt thermoplastics can be utilized. In onenon-limiting example, molten acrylonitrile butadiene styrene (ABS)plastic is used. In accordance with this disclosure, hot meltthermoplastic refers to a thermoplastic that is applied in a liquidstate and that forms an adhesive bond upon cooling to a solid state.

Although ABS plastic is one example, any of the following plastics canalso be used, alone or in combination with one another: Celluloid,Cellulose Acetate, Ethylene-Butyl Acrylate, Ethylene-Methyl Acrylate,Ethylene Vinyl Acetate (EVA), Ethylene Vinyl Alcohol (EVAL),Fluoroplastics (PTFEs, including FEP, PFA, CTFE, ECTFE, ETFE), lonomers,Liquid Crystal Polymer (LCP), Metallocene, Polyacetal (POM or Acetal),Polyacrylates (Melt and Cure Acrylics), Polyacrylonitrile (PAN orAcrylonitrile), Polyamide (PA or Nylon), Polyamide-imide (PAI),Polyaryletherketone (PAEK or Ketone), Polybutadiene (PBD), Polybutylene(PB), Polybutylene Terephthalate (PBT), Polybutylene Terephthalate(PET), Polycyclohexylene Dimethylene Terephthalate (PCT), Polycarbonate(PC), Polyketone (PK), Polyester, Polyethylene/Polythene/Polyethene,Polyether Block Amide (PEBA), Polyetheretherketone (PEEK),Polyetherimide (PEI), Polyethersulfone (PES), Polyethylenechlorinates(PEC), Polyimide (PI), Polylactic Acid (PLA), Polymethylpentene (PMP),Polyphenylene Oxide (PPO), Polyphenylene Sulfide (PPS), Polyphthalamide(PPA), Polypropylene (PP), Polystyrene (PS), Polysulfone (PSU),Polyvinyl Chloride (PVC), Spectralon, thermoplastic Olefinic Elastomer(TPO).

The thermoplastic pre-coating can be any of the foregoing hot meltthermoplastics or various blends thereof. The holt melt thermoplasticmay also incorporate secondary additives blended into said hot meltthermoplastic to impart specific enhancements to the precoating, theprecoated fibrous mat, or the resulting building panel. These secondaryadditives may provide improved strength, improved flexibility, improvedhardness, improved impact resistance, improved abrasion resistance, UVresistance, mold and mildew resistance, bacterial resistance, viralresistance, formaldehyde scavenging, carbon dioxide scavenging,structural characteristics, improved fire resistance, EMF resistance (asa shielding sheathing, interior wall board, roof deck board, orunderlayment), frequency specific resistance (as a shielding sheathing,interior wall board, roof deck board, or underlayment), solar collecting(as a roofing panel), piezoelectric energy generation (as anunderlayment), water drainage, or improved sound resistance.

The present disclosure also contemplates using any of a variety ofcoating devices 44. The preferred coating apparatus is a curtain coater48 and/or slot die coater and is illustrated in FIG. 4. However, a spraycoater 52 (FIG. 5) or a knife coater 54 (FIG. 6) can alternatively beused. The hot melt thermoplastic can alternatively be applied to thefibrous mat via a hot melt roll coater, forward, reverse, or multi-stageforward and reverse application methods. Still yet other alternativesinclude a hot melt slot coater, or a hot melt flow coater. An emersionbath can also be employed. Whatever coating device is employed, it ispreferred to position the coating device 44 in-line with the remainingcomponents of production line 20. In still yet other embodiments,off-line coating processes can be employed.

Whatever coating device 44 is used, a uniform layer 46 of the hotthermoplastic 38 should be applied in a continuous process. However, itis within the scope of the present invention to apply layer 46non-uniformly or to control the porosity layer 46. It is also preferredthat layer 46 be thin with a thickness of approximately 0-50% of thethickness of underlying mat 28. However, in the preferred embodiment,layer 46 has a thickness that is between approximately 1% to 10% of thethickness of mat 28. It is also preferred that thermoplastic layer 46have a minimum thickness weight of between approximately 0.01 g/sqft to45 g/sqft. FIG. 3 a illustrates the thermoplastic layer 46 applied toexternal surface 40 of mat 28. Once applied, layer 46 will generallycover between approximately 90% to 99.999% of the entire surface of mat28. Thus, even after layer 46 is deposited, approximately less than 1%and up to 90% of the underlying mat 28 will be exposed. This exposedregion will permit a limited degree of bleed through by the depositedslurry. FIG. 3 f is a bottom plan view showing the slurry bleedingthrough the surface of the board.

Coating device 44 may also include internal channels 56 within which aheating fluid, such as a hot oil from reservoir 57, may be circulated(note FIG. 4). These channels 56, thereby, act as a heat exchanger toraise or maintain the temperature of the plastic 38 prior to itsapplication. This ensures that thermoplastic 38 remains in a molten orliquefied state prior to its delivery upon mat 28. The coating head mayalso have electrically heated elements contained integrally or any othermeans of providing stable elevated temperature of said thermoplasticdelivery apparatus 44.

After thermoplastic layer 46 has been applied, mat 28 is routed overadditional guide rollers 42 prior to arriving at forming table 22. Thisgives the molten thermoplastic layer 46 sufficient time to come intocontact with the ambient air and cool. Layer 46, however, is still warmas it travels over forming table 22. Additionally, thermoplastic layer46 is permitted to adhere to the external surface 40 underlying mat 28,as well as to the individual fibers comprising mat 28, prior to formingtables 22.

Mat 28 with the applied thermoplastic layer 46 is also inverted prior toarriving at forming table 22. This inversion is achieved via one or moreguide rollers 42. More specifically, after thermoplastic layer 46 hasbeen applied, mat 28 is turned upside down to expose the internaluncoated surface 58 of mat 28. This results in thermoplastic layer 46contacting and facing underlying forming table 22. It also results ininterior surface 58 of first mat 28 being exposed. This is noted in thecross section of FIG. 3B.

Subsequent downstream processing may include the application of a firstgypsum slurry layer 62, and the passage of the slurry layer and matthrough a pair of roller coaters 64. This results in the creating of afirst dense slurry layer adjacent the exposed internal surface 58 offirst mat 28. Layer 46 will still be warm as first gypsum slurry layer62 is applied. Slurry 62, as well as the additional slurry that isdeposited downstream, will assist in cooling thermoplastic layer 46. Asslurry 62 is deposited, thermoplastic layer 46 is expanded and slightlydisplaced.

Vibrators 65 are preferably spaced along the length of forming tables 22to ensure the uniform distribution of slurry and the elimination ofvoids. The vibrators also act in embedding mat 28 within the depositedgypsum. Thereafter, additional gypsum slurry 66 is applied over theinterior surface 58 to form the core of building board 24 (note FIG. 3c). The deposited gypsum slurry 66 is preferably delivered from aoverhead mixer 36. Slurry 66 will act in further cooling and displacingthermoplastic layer 46. This, in turn, permits a thin layer of slurry 68to be formed between the external surface 40 of first mat 28 andthermoplastic layer or barrier 46 (FIG. 3 d).

As is known in the art, additives can be included in the gypsum slurryto achieve desired performance characteristics, such as polymers toprovide increased strength and reduced weight. One suitable polymeradditive is a styrene butadiene latex that is substantially stableagainst divalent ions.

The fibers of the first mat are sufficiently spaced to permit coreslurry 66 to fully penetrate the individual glass fibers. This ensuresthat individual fibers are coated and that mat 28 is completelypenetrated. This, in turn, results in the applied gypsum (62 or 66)coating the exterior surface 40 of mat 28. Thermoplastic coating 46,however, limits the amount of deposited slurry (62 or 66) that contactsthe forming belts 22. In this manner, thermoplastic coating 46 acts as abarrier preventing the discharge of slurry from the exterior surface 40of mat 28. This prevents forming table 22, as well as associated belts,pulleys, and motors, from getting contaminated by gypsum or gypsumparticles.

Thermoplastic barrier 46 and thin gypsum layer 68 together prevent fiberdisengagement from mat 28. Barrier 46 and layer 68 also impart desiredphysical properties to the resulting building board 24. FIG. 3C is across section of board 24 immediately after the gypsum slurry 66 hasbeen applied to interior surface 58. As noted, slurry 66 does notimmediately penetrate mat 28. FIG. 3D is a depiction of the subsequentcross section after gypsum slurry 66 has had time to fully penetrate thethickness of mat 28 and encounter thermoplastic barrier 46. Becauselayer 46 is only applied to between 90% to 99.999% of mat 28, a limitedamount of slurry 66 will bleed through to the external surface of thebuilding board.

Thereafter, a second length of mat 32 is deposited over top of gypsumslurry core 66. This second mat 32 can likewise comprise a plurality ofnon-woven randomly aligned glass fibers. Second mat 32 may have a smallvolume of gypsum 72 applied to its surface before it is applied togypsum core 66. Thereafter the resulting panel 24 is formed into adesired thickness by way of a forming plate 74 and pinch point 76.

In accordance with conventional gypsum board manufacturing techniques,the resulting panel is then delivered to a series of board dryers 26(FIG. 2). Dryers 26 are utilized heating the gypsum slurry within thepanels and vaporizing any non-crystalline water. Four dryer zones arepreferably included. However, the number of dryer zones employed is notcritical to the present invention. Dryers are designed to heat thebuilding boards 24 to a degree sufficient to cure the gypsum. This istypically achieved at a temperature of approximately 212° F. Thepresence of entrained water within the gypsum core will delay thetemperature of the gypsum core from raising above 212° F. Dryers of thedepicted embodiment utilize a conventional construction and run attemperature levels that range anywhere between approximately 180° F. to650° F., which is typical for gypsum drying operations. As a result ofthis heating process, water is vaporized at the surface and deliveredupwardly through second mat 28. Panel 24 can then be cut to desiredlengths depending upon the intended use. Notably, thermoplastic layer 46is not dissolved in dryers 26 and remains intact upon the final cutpanels 24.

The present disclosure includes that contained in the appended claims,as well as that of the foregoing description. Although this inventionhas been described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

What is claimed is:
 1. A system for manufacturing building boards alonga production line, the system comprising: a roll of a first glass mat,the first mat having interior and exterior surfaces; a coating apparatusand a supply of a hot melt thermoplastic, the coating apparatus beingused to apply a thin layer of the hot melt thermoplastic on the exteriorsurface of the first glass mat; guide rollers for inverting the firstglass mat after the application of the hot melt thermoplastic, the guiderollers allowing the applied thermoplastic coating to partially cool; aseries of forming tables positioned downstream of the coating apparatus,the guide rollers delivering the first mat with the thermoplasticcoating to a forming table, wherein the adhered thermoplastic coatingfaces the forming table and the interior surface of the first mat isexposed.
 2. The system as described in claim 1 further comprising amixer positioned downstream of the coating apparatus, the mixer storinga volume of slurry and having an outlet for depositing the slurry overthe interior surface of the first mat, wherein the thermoplastic coatingacts as a barrier in preventing deposited slurry from contacting theunderlying forming belt.
 3. The method as described in claim 2 whereinthe deposited gypsum slurry is permitted to fully penetrate the firstmat, wherein the deposited gypsum slurry forms a small layer between thecontacting surface of the first mat and the thermoplastic coating. 4.The system as described in claim 2 further comprising a roll of a secondmat, the second mat being applied over the gypsum slurry, wherein thefirst mat, the second mat, the gypsum slurry and the thermoplasticcoating together form a panel.
 5. The system as described in claim 1wherein the coating apparatus is in-line with the production line. 6.The system as described in claim 1 wherein the coating apparatus is acurtain coater.
 7. The system as described in claim 1 wherein thecoating apparatus is a spray coater.
 8. The system as described in claim1 wherein the coating apparatus is a knife coater.
 9. The system asdescribed in claim 1 wherein the coating apparatus is a slot die. 10.The system as described in claim 1 wherein the thermoplastic is providedin a layer having a thickness weight of between approximately 0.01g/sqft to 45 g/sqft.
 11. A system for manufacturing building boards, thesystem utilizing a forming table and a mixer for supplying a slurry, thesystem further comprising: a roll of a mat, the mat having interior andexterior surfaces; a coating apparatus positioned in-line with theforming table and the mixer, the coating apparatus containing a supplyof a thermoplastic and functioning to supply a layer of thethermoplastic on the exterior surface of the mat.
 12. The system asdescribed in claim 11 further comprising guide rollers for inverting themat after the application of the thermoplastic, the guide rollersallowing the applied thermoplastic coating to partially cool.
 13. Thesystem as described in claim 11 wherein the thermoplastic is a hot meltthermoplastic.
 14. The system as described in claim 11 wherein thethermoplastic is applied via a curtain coater.
 15. The system asdescribed in claim 11 wherein the thermoplastic is a moltenacrylonitrile butadiene styrene (ABS).
 16. A method as described inclaim 1 wherein the first mat and the second mat are precoated withthermoplastic.
 17. A method as described in claim 1 wherein either thefirst mat or the second mat is precoated with thermoplastic.